The present invention is based on Japanese Patent Application No. 2000-174319, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a waste-heat gas driven cogeneration system using waste-heat gas generated from a micro gas turbine so that a cold heat output can be obtained efficiently.
2. Description of the Related Art
Public attention has been paid to a micro gas turbine electric power plant as a distributed electric source recently. The plant uses natural gas or biogas as fuel and the fuel is burned to operate a small-sized gas turbine to thereby generate electric power. However, it cannot be said that energy efficiency in the plant is sufficiently high. Because a large amount of energy is lost as waste heat into exhaust gas, it may be said that the plant is adapted to a cogeneration system for recovering waste heat and using it efficiently. In the background art, a cogeneration system for obtaining hot water by use of waste heat has been proposed from this point of view.
In the background-art cogeneration system for obtaining hot water, however, total efficiency is low and it is hardly worth using the cogeneration system when there is no need for hot water.
On the other hand, electric power is in great demand particularly in the field of freezers and coolers in summer, so that public hopes are put on a cogeneration system capable of supplying cold heat also from the point of view of leveling electric power. From this point of view, there may be conceived a method in which steam is generated from waste-heat gas to thereby operate a freezer using lithium bromide. It is however impossible to obtain a coolant at a temperature not higher than 5xc2x0 C. because water is used as a coolant theoretically in this method. It is therefore difficult to apply this method to refrigeration. On the other hand, it is conceived that this method is applied to an ammonia absorption type refrigerator in which a coolant in a freezing temperature range can be obtained by use of steam.
Ammonia to be used as a coolant in this refrigerator is however harmful to the human body. Leaking of ammonia to the outside may be caused by corrosion or the like, if a material to be used is selected by mistake. If leaking of ammonia to the outside occurs once, there is a problem in worries about damages such as very great damage to the human body, an offensive odor deposited on peripheral goods and particularly prohibition against foods. It cannot be said that this system is adapted for small-scale industry and private use expected as a distributed electric source. It is conceived that application of this system to private districts and the field of foods is difficult practically.
The present invention is designed upon such circumstances as the background and an object of the present invention is to provide a waste gas-driven cogeneration system in which thermal energy is obtained effectively from waste heat of exhaust gas generated from a micro gas turbine so that the thermal energy can be used as a driving source to generate cold heat for refrigeration or cooling.
That is, in order to solve the above object, according a first aspect of the present invention, there is provided a cogeneration system using micro gas turbine waste-heat gas, comprising: a micro gas turbine; a driving portion having a high-temperature-side hydrogen storage alloy container and for operating through direct or indirect heat exchange between the high-temperature-side hydrogen storage alloy container and waste-heat gas from the micro gas turbine and a cold-heat heat medium to thereby absorb and release hydrogen; and a cold heat output portion having a low-temperature-side hydrogen storage alloy container and for absorbing and releasing hydrogen by use of the low-temperature-side hydrogen storage alloy container in accordance with the operation of the driving portion to generate cold heat, transmit the cold heat to a cooling heat medium to thereby externally supply the cold heat through the cooling heat medium.
According to a second aspect of the present invention, in the cogeneration system using micro gas turbine waste-heat gas as defined in the first aspect, the heat exchange between the waste-heat gas from the micro gas turbine and the high-temperature-side container is performed indirectly through steam generated by heat of the waste-heat gas.
According to a third aspect of the present invention, in the cogeneration system using micro gas turbine waste-heat gas as defined in the first or second aspect, the driving portions and the cold heat generating portions are provided multistageously respectively so that waste-heat gas subjected to heat exchange in the pre-stage driving portion is further subjected to heat exchange in the post-stage driving portion to thereby make the post-stage driving portion operate.
According to a fourth aspect of the present invention, in the cogeneration system using micro gas turbine waste-heat gas as defined in the third aspect, heat exchange is performed between the waste-heat gas from the micro gas turbine and the pre-stage high-temperature-side container indirectly through steam generated by heat of the waste-heat gas whereas after the heat exchange, and further heat exchange is performed directly between the waste-heat gas after the first heat exchange and the post-stage high-temperature-side container.
According to a fifth aspect of the present invention, the cogeneration system using micro gas turbine waste-heat gas, as defined in any one of the first through fourth aspects, further comprises a hot water generator for generating hot water by performing heat exchange between water of the hot water generator and the waste-heat gas after the waste-heat gas is subjected to the heat exchange in the driving portion.
According to the present invention, waste heat generated from the micro gas turbine is used as a driving source. To use such waste heat, direct or indirect heat exchange is performed between exhaust gas with the waste heat, that is, waste-heat gas and a high-temperature-side hydrogen storage alloy container to thereby recover thermal energy.
Incidentally, for improvement of energy efficiency in the micro gas turbine, the temperature is raised by heat exchange between air taken in the turbine and the waste-heat gas to thereby improve power generating efficiency. As a result, the temperature of the waste-heat gas finally discharged from the micro gas turbine becomes low about 300xc2x0 C. As described above, a cogeneration system for recovering heat from waste-heat gas and recycling the heat in order to improve energy efficiency in the micro gas turbine plant has been discussed. In the existing situation, nothing but hot water can be obtained because the temperature of waste-heat gas is low as described above. Hence, cold heat necessary for use in coolers and refrigerators particularly in summer cannot be obtained.
According to a first embodiment of the present invention, waste-heat gas by which the background-art heat-driving type cooler system cannot be driven is imported from the micro gas turbine and subjected to direct heat exchange with the hydrogen storage alloy container to thereby generate cold heat. Hence, a refrigeration output can be obtained in a freezing temperature range which can be adapted for small-scale industry and private use, food industry use, etc. This system can be used as a high-energy-efficiency system in a food factory, a convenience store, a supermarket, a hospital, a hotel, or the like. Moreover, this system can be provided as a cogeneration system using a micro gas turbine free from any problem in leaking an offensive odor, or the like.
According to a second embodiment of the present invention, waste-heat gas at a high temperature without heat exchange with intake air can be used to make it possible to attain improvement of energy-utilizing efficiency though power generating efficiency in the micro gas turbine is reduced. That is, heat exchange is performed between high-temperature waste-heat gas generated from the micro gas turbine and a heat medium so that the driving portions in the present invention can be operated by the heat medium with heat energy.
This is equivalent to the second aspect of the present invention. Steam is used as the heat medium so that indirect heat exchange is performed between the waste-heat gas and the high-temperature-side hydrogen storage alloy container. Also in this embodiment, the waste-heat gas can be used as a driving source to drive a refrigeration system using hydrogen storage alloy. Hence, a refrigeration output which can be adapted for small-scale industry and private use, food industry use, etc. can be obtained. Incidentally, in this system, waste-heat energy is transmitted to another heat medium. Hence, even in the case where the condition for generating waste gas varies in accordance with the start and stop of the heat micro gas turbine, there is an advantage in that the instability of the cold-heat output caused by the change of the condition can be eliminated if measures to store thermal energy and reserve it once are taken.
Further, the driving portions and the cold-heat generating portions may be provided multistageously so that waste-heat gas subjected to heat exchange in each of the front-side driving portions can be further subjected to heat exchange in each of the post-stage driving portions.
In this embodiment, thermal energy remaining in the waste-heat gas used in the pre-stage can be used. Hence, total efficiency is improved, so that a refrigeration output which can be taken out increases. Preferably, after waste-heat gas the temperature of which is high is subjected to indirect heat exchange with each of the alloy containers through a heat medium such as steam in each of the pre-stage driving portions, the low-temperature waste-heat gas discharged is further subjected to direct heat exchange in each of the post-stage driving portions.
Moreover, waste-heat gas subjected to heat exchange in the driving portions is used so that hot water is obtained by a hot water generator. Because hot water is obtained in addition to the cold-heat output, total efficiency is improved more greatly. This embodiment can be applied to any one of the first, second, third and fourth aspects of the present invention.
Incidentally, in any aspect of the present invention, high-temperature-side hydrogen storage alloy containers and low-temperature-side hydrogen storage alloy containers are provided. A hydrogen storage alloy adapted to the operation of each of the containers is contained in the container. That is, it is necessary on the high-temperature side that hydrogen is released by waste-heat gas and absorbed by a cooling heat medium where as it is necessary on the low-temperature side that desired cold heat is generated by release of hydrogen. Each of the hydrogen storage alloys to be used in the present invention is not limited to a specific kind if the alloy satisfies these requirements. That is, any suitable alloy can be selected.
These hydrogen storage alloys are contained in the alloy containers respectively so that hydrogen can be absorbed and released. Absorption and release of hydrogen can be achieved when an aeration material is disposed in the container or a ventilation passage is secured to thereby make it possible to move hydrogen. Each of the alloy containers is generally made of a material having a shape adapted to heat exchange and having good heat conducting characteristic so that heat exchange can be performed between waste-heat gas generated from the micro gas turbine and the cooling heat medium. The configuration of each of the alloy containers is considered in accordance with whether heat exchange with the waste-heat gas is performed directly or indirectly.
The driving portions include the high-temperature-side containers respectively among the aforementioned containers. In each of the high-temperature-side containers, the container makes heat exchange with the waste-heat gas and the cooling heat medium directly or indirectly. Therefore, each of the driving portions is configured so that waste-heat gas or a heat medium substituted for the waste-heat gas and a cooling heat medium are imported into the driving portion. These heat media touch the aforementioned containers to thereby perform heat exchange. The driving portions are operated by the heat exchange to thereby absorb and release hydrogen. The absorbed and released hydrogen moves as a driving force between a driving portion and a corresponding cold-heat generating portion which will be described below. Therefore, a driving portion and a corresponding cold-heat generating portion are generally connected to each other by a hydrogen-travelling passage.
On the other hand, the cold-heat generating portions include the low-temperature-side containers respectively among the aforementioned containers. When cold heat is generated in each of the low-temperature-side containers, the cold heat is transmitted to the cold-heat heat medium. The cold heat is delivered to an external heat-utilizing portion by this heat medium or by a heat medium after further heat exchange. Although a refrigerator for storing foods is taken as an example of the cold heat-utilizing portion, the present invention is not limited thereto and can be applied to any apparatus which needs cooling or refrigeration.